How to Install a Spin-In Duct Fitting

Spin-in fittings connect flex duct to a duct trunk line.

Spin-in collars reduce the installation time of a duct branch line by eliminating the need for screws to hold it in position. Instead, the collars sandwich the duct wall between an inner collar and an outer tapered bead. The correct hole size is required to ensure the spin collar sits securely in the wall of the duct. Once correctly installed, the spin-in collar will provide a fail-safe connection between a duct trunk line and the air register distributing air throughout your home.

Determine Spin-in Diameter

Measuring the diameter of the spin-in is the first step in ensuring it fits correctly in the duct. Taking the measurement from the wrong end of the fitting will cause you to receive a false dimension that will lead to an incorrectly cut hole. Always measure the fitting from the end of the fitting with the taper and then add 1/8 inch to the diameter, to allow room for the fitting to spin in the duct.

Cut and Prepare the Hole

After measuring the hole, a hole cutter is required to ensure you cut a round hole in the side of the duct. The hole cutter consists of a graduated arm, a three-sided drill bit and a pivot point. After moving the pivot point, the smooth end of the drill bit fits into a drill motor. Rotating the cutter slowly will cut a perfectly round hole in the sheet metal. A 1/2-inch slit is required after cutting, to allow the inner collar to slide through the duct wall.

Secure the Spin-in Collar

Securing the spin-in collar in the duct requires sliding the edge of the inner collar into the cut slit and spinning the fitting clockwise. After one full revolution, the inner collar will pop through the duct and the spin-in collar will sit loosely in the duct. After installation, you set the handle in an accessible location, then pull the inner flange to the bottom of the tapered bead by squeezing them together -- at multiple locations -- with a pair of self-locking pliers to lock it in position.

Seal the Collar Edges

Even a tight spin-in collar will leak air around its connecting point to the ductwork. Apply a water-based sealant to the bottom of the collar with a paintbrush to stop air leaks. The sealant requires 24 hours to harden; during this time, you cannot run the air conditioning system.

About the Author

Ely Hauser is a union tradesman with more than 20 years of experience in the construction industry. He has also been a writer since 2002, contributing to the "Brazoria County Facts" newspaper, as well as various outdoor and construction websites.